Silver, copper, mercury, cadmium and zinc ions are known urease inhibitors; see, for example, Kaneshiro et al., Arch. Biochem. Biophys. 174 647-650 (1976) and Geike, Z. Anal. Chem. Band 258, Heft 4, 284-285 (1972). Practical applications disclosed include the quantitative analysis of these metals with urease (e.g. the Geike reference cited above), and the use of copper salts as additives to urea fertilizer to prevent its decomposition (U.S. Pat. No. 3,523,018, issued Aug. 4, 1970, to Geissler et al).
The use of copper and/or silver metal for preventing the development of malodors has been disclosed in British Pat. No. 1,581,586, issued Dec. 17, 1980 to Yamouchi (footwear comprising a resin containing powdered copper, silver or a Cu-Ag alloy); French Demande No. 2,259,620, published Aug. 29, 1975, Hansson (treatment of e.g., liquid cow manure with a solution containing HNO.sub.3, a nitrite and CuSO.sub.4); and Japanese Specification No. 74/27,035, July 13, 1974, Okahima, et al. (bentonite clay impregnated with Cu(NO.sub.3).sub.2 and AgNO.sub.3 and subsequently dried and oxidized, for use in tanks for carrying urine).
Prior art attempts to deodorize cat litter include the addition of a perfume (see, e.g., U.S. Pat. No. 3,921,581, issued Nov. 25, 1975 to Brewer), and the addition of chlorophyll, mainly in the form of dried alfalfa to the litter, (see, e.g., U.S. Pat. No. 3,923,005, issued Dec. 2, 1975 to Fry et al., assigned to The Clorox Company).
U.S. Pat. No. 4,129,094, issued Dec. 12, 1978 to Stockel, discloses the use of fly ash, bottom ash and/or boiler slag as cat litter materials. The composition of fly ash, as determined by the ASTM and cited in the patent, includes silicon dioxide, alumina, ferric oxide, calcium oxide, magnesium oxide, sodium oxide and potassium oxide. The material is not reported to contain any of the Group Ib or IIb transition metals.